In some applications, it is desired to calibrate an image capture device (e.g., a digital camera) so that the colors of the image (i.e., measured colors) will more accurately correspond to the actual colors (i.e., scene radiance) received by the image capture device (also referred to herein simply as a device).
FIG. 1 (Prior Art) shows an example of a system 100 that includes a digital camera 102 having a response function 104. In operation, digital camera 102 captures an image of a scene 106 (via its scene radiance) and outputs measured colors that are used to form a digital image 108. The measured colors of digital image 108 are related to the scene radiance by response function 104 (also referred to as the radiometric response). In general, response function 104 is non-linear and depends on the camera. Further, the response function can be different even if the cameras are the same model.
Camera 102 can be calibrated by finding the “inverse” of response function 104 so that, ideally, the measured colors will be mapped into colors exactly matching the scene radiance. In one type of approach, a user takes an image of a “reference” color scene (i.e., having regions of known color) so that the measured colors output by camera 102 can be compared to the actual colors. Thus, this type of approach requires an image of the “reference”. In another type of approach, several images of a scene are required. In one particular approach, the series of images are taken under various precisely known exposure settings, with all of the images being registered (i.e., taken with the positions of the camera and scene being unchanged).
However, these conventional solutions have shortcomings in that in some scenarios, neither a “reference” image captured by the camera nor a series of registered images with different exposure settings may be available. For example, in some scenarios, only an image may be available, with no knowledge of the camera and the exposure setting used to capture the image.